USB: serial: remove vizzini driver

It's out-dated for the tty-layer stuff, and would require a bunch of
work.  That's not really a big deal, the big issue is that there is no
company contact for the hardware, so questions we have about it (like
why isn't this just handled by the cdc-acm driver instead?) go
unanswered.

So drop the driver.  If someone comes along to help answer the
questions, we can easily revert this and fix up the code.

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Rob Duncan <rob.duncan@exar.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>